Frequency modulation and frequency-to-voltage converters which detect the information in a frequency modulated signal are part of an old and well-established art. It is virtually impossible to provide a brief statement of the prior contributions of others to this art because such a wide variety of signal processing techniques have been suggested previously.
Although the frequency modulation art is old and well-established, the circuitry commercialized in the past for detecting the information in frequency modulated signal suffers from certain shortcomings. A major problem is that variations in the values of circuit components, caused for example by environmental changes, component aging and manufacturing tolerances, introduce errors in the accuracy of the output signals. This affects the ability of the frequency detector circuitry to interface effectively with other processing circuitry.